dentistry journal Article Evaluation of Lower Dental Arch Crowding and Dimension after Treatment with Lip Bumper versus Schwarz Appliance. A Prospective Pilot Study Vincenzo Quinzi 1 , Silvia Caruso 1, Stefano Mummolo 1,* , Alessandro Nota 2 , Anna Maria Angelone 1, Antonella Mattei 1 , Roberto Gatto 1 and Giuseppe Marzo 1 1 Department of Health, Life and Environmental Science, University of L’Aquila, Piazza Salvatore Tommasi, 67100 L’Aquila, Italy; [email protected] (V.Q.); [email protected] (S.C.); [email protected] (A.M.A.); [email protected] (A.M.); [email protected] (R.G.); [email protected] (G.M.) 2 Dental School, Vita-Salute San Raffaele and IRCCS San Raffaele Hospital, 20132 Milan, Italy; [email protected] * Correspondence: [email protected] Received: 11 March 2020; Accepted: 7 April 2020; Published: 10 April 2020 Abstract: Aim: The treatment of patients with mixed dentition, with inferior moderate dental crowding (the so-called borderline cases, between extraction and expansion) is not yet clear. Two examples of widely used appliances for increasing lower dental arch dimensions are the Schwarz’s appliance and lip bumper. The aim of this prospective study was to compare dental crowding and arch dimensions from pre- to post-treatment with lip bumper versus Schwarz’s appliance. Subjects and Methods: Pre- and post-treatment orthodontic records of twenty subjects (10 males and 10 females) were analyzed in the present study. Inclusion criteria were: first/second molar class malocclusion; crowding of the mandibular arch, from mild to moderate (4–6 mm); mixed dentition; age 9 years ≤ at the beginning of the treatment; stage CS1 or CS2 of maturation of the cervical vertebrae analysis (CVM) at the beginning of the treatment. Ten subjects were treated with a lip bumper, and ten with the removable Schwarz appliance. The primary outcomes were the variations in dental crowding and arch dimensions from pre- to post-treatment. Results: Both the two appliances caused a statistically significant mean improvement/reduction in crowding, of 3.5 mm and 2.9 mm, for the Schwarz appliance and lip bumper, respectively. The Schwarz appliance resulted more effective in increasing arch dimension at the intercanine level, and arch perimeter, while the lip bumper achieves a higher increase in arch length. Conclusions: A lip bumper and Schwarz appliance are both useful in reducing crowding in mixed dentition. This improvement is due to the increase in dental arch dimensions, although the distribution of space resulted slightly differently between the two appliances. Keywords: mixed dentitions; interceptive orthodontics; preventive orthodontics; corrective orthodontics; dental arch; mandible 1. Introduction Crowding is the most frequent form of malocclusion, as stated in the United States at the turn of the 1990s, when a study on the prevalence of dental malocclusions was conducted in a sample of 14,000 subjects representing the American population in the context of the N.H.A.N.E.S. III (National Health and Nutrition Estimates Survey) [1]. In that survey, the prevalence of crowding was observed in about 45% of children in mixed dentition, and in 66.5% of subjects aged from 18 to 50 years. A similar prevalence of crowding in mixed dentition was also reported in the Italian population [2–4]. Therefore, Dent. J. 2020, 8, 34; doi:10.3390/dj8020034 www.mdpi.com/journal/dentistry Dent. J. 2020, 8, 34 2 of 9 crowding is considered a malocclusion that never self-corrects, as rather it worsens over time. If present in deciduous teeth, it will worsen in the next two dental stages [5]. In general, during the years following the completion of dentition [6], it worsens and involves 50% of individuals who were exempt from it during their first decade of life [1]. The worsening of the crowding seems to occur concomitantly with the physiological decrease in the length of the dental arches, and is associated with aesthetic as well as periodontal problems [7,8], mostly in adults [9] and with other malocclusions, such as crossbite [10,11], class II malocclusion [12,13], or temporomandibular joint dysfunction [11,14,15]. In the past 100 years, the debate between the two treatments of crowding—extracting teeth or dental arches expansion—has not yet seen a universal winner among modern orthodontists. In patients with slight or severe dento-alveolar discrepancies, the choice between extracting teeth or gaining space with suitable techniques, such as the use of mini-screw anchorage [16], is clear [17]. On the other hand, the path to follow for those patients with moderate dental crowding, the so-called borderline cases, is less clear. The “extraction or non-extraction” controversy arises from when Edward Angle opposed the extraction treatment because of a purely anatomical observation, that was that the lower jaw does not have a violable suture line. Consequently, if in the upper arch it was therefore possible to increase the transverse diameters by separating the mid-palatine suture, this was not practicable in the lower arch. So, although rapid palatal expansion has shown to be able to induce significant changes also in the mandibular arch, through a change in the tongue position [18–21], which tends to improve its diameter—often compressed in the contracted maxilla—this is not always sufficient to resolve larger crowdings [22]. A space-saving procedure in the lower arch in patients with mixed dentition is possible with devices that induce a remodeling of the alveolar bone, and an improvement of teeth inclination in the posterior sectors, where they are often too lingualized. This procedure usually translates into an increase in arch perimeters and transverse dimensions of the lower dental arch. One of the most used appliances is the lip bumper (LB), which alone can obtain flaring of the mandibular incisors, distalization and uprighting of the mandibular first molars, and buccal expansion of the canines, premolars, and molar transverse diameters. Lip forces are transmitted through this appliance onto the molars [23]. It has been stated that intermolar and interpremolar changes with a LB during mixed dentition can be considered as the best predictors for post-retention mandibular dental arch stability, as for every millimeter of increase in the intermolar and interpremolar widths there was a 1.52 and 2.70 times increase, respectively, in the odds of having stability. There was also weak evidence for the influence of gender [24]. Another appliance used is the Schwarz appliance (SA), a removable plate that primarily affects the dento-alveolar complex, while it has little effect on either mandibular bodies [25]. The SA is also used for the expansion of the upper arch [26]. The purpose of this clinical trial was to evaluate the dimensional variations of the mandibular arches in patients with mixed dentition affected by mild to moderate dental crowding, treated with two different types of orthodontic devices—the LB and the SA. 2. Materials and Methods The present protocol was approved by the Ethics Committee of the University of L’Aquila (Document DR206/2013, 16 July 2013). Written consent was obtained from all the participants (patient’s parents/legal guardians). Twenty patients (10 males and 10 females), referred to the Department of Orthodontics, University of L’Aquila (Italy) for orthodontic needs, were enrolled in the present study. Ten subjects were treated with LB (Figure1), and ten with the removable SA (Figure2). Dent. J. 2020, 8, 34 3 of 9 Dent.Dent. J. 2019 J. 2019, 7, ,x 7 FOR, x FOR PEER PEER REVIEW REVIEW 3 of3 9 of 9 FigureFigure 1. Lip 1.1. Lip bumper bumper appliance. appliance. Figure 2. Schwarz appliance. FigureFigure 2. Schwarz2. Schwarz appliance. appliance. The assignment to either study group took place by simple randomization with sealed envelopes. The assignment to either study group took place by simple randomization with sealed TheThe inclusion assignment criteria to foreither this studystudy were:group first took/second place molar by simple class malocclusion, randomization mild with to moderatesealed envelopes. The inclusion criteria for this study were: first/second molar class malocclusion, mild to envelopes.crowding The of theinclusion mandibular criteria arch for (4–6this study mm), mixedwere: first/second dentition, age molar9 class years malocclusion, at the beginning mild of to the moderate crowding of the mandibular arch (4–6 mm), mixed dentition,≤ age ≤ 9 years at the beginning moderatetreatment, crowding and stage of CS1the mandibular or CS2 of maturation arch (4–6 ofmm), the cervicalmixed dentition, vertebrae age analysis ≤ 9 years (CVM) at the at the beginning beginning of the treatment, and stage CS1 or CS2 of maturation of the cervical vertebrae analysis (CVM) at the of ofthe the treatment, treatment. and stage CS1 or CS2 of maturation of the cervical vertebrae analysis (CVM) at the beginning of the treatment. beginningPatients of the who treatment. underwent previous orthodontic treatments, presented craniofacial anomalies, or Patients who underwent previous orthodontic treatments, presented craniofacial anomalies, or underwentPatients who teeth underwent extraction treatmentsprevious orthodontic were excluded. treatments, presented craniofacial anomalies, or underwent teeth extraction treatments were excluded. underwentMeasurements teeth extraction were takentreatments on the were plaster excluded. models before and after treatment with a digital caliper, Measurements were